OTcl

OTcl, short for MIT Object Tcl, is an extension to Tcl/Tk for
object-oriented programming. It shouldn't be confused with the IXI
Object Tcl extension by Dean Sheenan. (Sorry, but we both like the
name and have been using it for a while.)

Some of OTcl's features as compared to alternatives are:

designed to be dynamically extensible, like Tcl, from the ground up

builds on Tcl syntax and concepts rather than importing another language